Deduplication

Deduplication refers to a process in Backblaze Computer Backup that prevents files from being unintentionally duplicated in your online backup. Files are digitally fingerprinted (checksummed) before they are sent to the server. When a file's fingerprint (SHA-1 checksum) matches an already backed up file, it is updated at the Backblaze servers rather than re-transmitted.

When you copy or move a file to a different location on your computer (including drive-to-drive), Backblaze considers it a new file and queues it for upload to the Backblaze servers. However, after the file is received by the Backblaze servers, if the file's data and filename are identical to the data and filename of a file that is stored in your online backup, then the server does not create a duplicate version of the file. It just updates the location of the file in your backup to match the current location of the file on your computer.

You may see these files queued for back up, but when any given file is at the front of the queue, it is checksummed, compared against the existing backup, and deduplicated resulting in the file updating on the server rather than re-uploading.

For example, you have a file named GrandCanyon.png that was stored in the Downloads folder on your computer for long enough that Backblaze uploaded the file as part of your online backup. Later, you move that file to the Pictures folder on your computer. When Backblaze detects the move and then uploads the file to your backup, the server detects that this is the same file as the GrandCanyon.png file that is stored in your online backup in the Downloads folder. So, the server does not create a duplicate of the file in the Pictures folder. It will simply update the location of the file in your online backup, changing it from the Downloads folder to the Pictures folder.

Depending on the size of your file, it may take awhile before you can see the file's updated location within your online backup.